This invention relates to an apparatus for removing urea and other toxins in the dialysate (dialyzing fluid) used for artificial kidneys otherwise referred to as hemodialyzers.
The artificial kidney is an apparatus for removing toxins (toxic waste metabolities) such as urea, creatinine, and uric acid from the blood of the patient of chronic uremia. In the hemodialyzing system, which is the most commonly used type of the artificial kidney, the blood from the artery of the patient is passed through a hemodizlyzer and is returned to the vein. The dialysate flows through the hemodialyzer and with the dialysate being separated from the blood by a conventional membrane such as cellophane, urea and other toxins in the blood are transferred into the dialysate by dialysis, that is, diffusion through the membrane.
The dialysate is an aqueous solution of various salts, glucose, and others, having an osmotic pressure approximately equal to that of blood. Since the driving potential for dialysis is the difference in concentration of urea and other toxins across the membrane, the rate of dialysis per unit area of the membrane in a given hemodialyzer varies in proportion to these concentration differences under given operating conditions such as blood and dialysate flow rates.
In a batch system with a dialysate tank, within which a certain amount of dialysate is recirculated, the rate of dialysis decreases as time goes on because the concentrations of urea etc. in the dialysate increase and consequently also the differences in the concentrations of toxins across the membrane decrease with time. In the conventional flow system, which is commonly adopted to avoid such increase in the concentrations of urea etc. in the dialysate with time, a fresh dialysate which does not contain urea etc. is continuously supplied to the hemodialyzer, and the dialysate leaving the hemodialyzer which contains urea etc. is discarded. However, this type of flow system requires a large quantity of dialysate, because hemodialysis usually must be conducted for as long as 8 to 12 hours. For example, if hemodialysis lasts 10 hours with a blood flow rate of 200 ml per minute and a dialysate flow rate of 500 ml per minute, the total amount of dialysate required will be 300 liters.
A batch system in which dialysate is recirculated within a tank would also require a large amount of dialysate if the increase in the concentrations of urea etc. in the dialysate is to be minimized. Thus, the cost of the dialysate is substantial. Also, it is not desirable to store such a large amount of prepared dialysate because of possible risk of bacterial contamination.
A commonly adopted procedure is to prepare dialysate by continuous dilution of a dialysate concentrate having a concentration approximately 35 times that of the dialysate, using tap water. However, such a continuous dilution system requires various complicated, expensive components including a proportioning pump. One of the reasons for the high cost of the conventional artificial kidney device is the use of such an expensive system for the continuous dilution of dialysate concentrate in the preparation of dialysate.
To solve this problem of the artificial kidney system requiring a large quantity of dialysate, it would be possible to remove urea etc. by appropriate means from the dialysate which is recirculated through a means in which urea etc. are removed. However, there has been no efficient system for such procedure. It is relatively easy to remove uric acid and creatinine from the dialysate by adsorption on an adsorbent such as activated charcoal or alumina. However, since any adsorbent adsorbs only a relatively small amount of urea due to the unfavorable equilibrium relationship for activated charcoal, a batch adsorption system requires a large amount of adsorbent. Also, it is inevitable in such a batch adsorption system that urea remains in the dialysate at a substantial concentration.
To remedy this shortcoming, Blaney et al. (Chemical Engineering Progress Symposium Series, No. 84, Vol. 4, p. 112-120 (1968)) proposed a system in which the dialysate is passed through a single bed of adsorbent which adsorbs toxins in the dialysate. After adsorption is completed, the toxins are desorbed from the adsorbent by passing water through the absorbent bed. This type of system in which a single bed of adsorbent is used to adsorb and desorb toxins in the dialysate in inefficient for the reasons mentioned subsequently and requires a relatively large amount of adsorbent.
It is accordingly an object of the present invention to provide an efficient and effective artificial kidney system using a recirculated dialysate and a plurality of adsorbent beds that permit substantially continuous adsorption and continuous desorption.
This and other objects of the present invention may be readily apparent from a perusal of the following description including the drawings.